SUMMARY ? Project 1 Despite the tremendous promise of cerebral organoid technology for studying human brain development, modeling brain diseases and testing drug efficacy, we are still at the beginning of an era to engineer mini- brains from human stem cells. For broad applications in basic and translational research, organoid development should be scalable, cost efficient and highly consistent. Previous methods are largely based on cell self-assembly with little external control, and organoids generated by this approach exhibit large variability from sample to sample. We recently developed a miniaturized bioreactor and a protocol to generate forebrain- specific organoids from human iPSCs. These organoids recapitulate key features of human cortical development, including progenitor zone organization, neurogenesis, and gene expression. We employed the forebrain organoid platform to model Zika virus (ZIKV) exposure and showed that preferential, productive infection of neural progenitors by ZIKV leads to increased cell death and reduced proliferation, resulting in decreased neuronal cell-layer volume resembling microcephaly. In this collaborative research Center, we will investigate the effects of ZIKV and West Nile virus infections at different time points of organoid development to evaluate our platform with two different neurotropic flaviviruses that may target different stages of neural development. Project 1 will focus on technology development to reduce organoid heterogeneity and allow for quantitative analyses of the effects of different viruses on organoid development. To model later stages of brain development, we will adopt state-of-the-art bioengineering approaches to improve the diffusion of media to the organoids and reconstitution of different cell types. And finally, we will develop a medium-throughput platform for compound testing and perform a pilot assay using compounds with known biological effects on viral-infected cells.